| Propylene (n.) A colorless gaseous hydrocarbon (C3H6) of the ethylene series, having a garlic odor. It occurs in coal gas, and is produced artificially in various ways. Called also propene. |
| propylene glycol / propanediol a sweet colorless, viscous, hygroscopic liquid used as an antifreeze and in brake fluid and also as a humectant in cosmetics and personal care items although it can be absorbed through the skin with harmful effects |
| propylene / propene a flammable gas obtained by cracking petroleum, used in organic synthesis |